Fuel-fired, storage-type water heaters often include a combustion chamber and air plenum disposed below a water tank. A burner element, fuel manifold tube, ignition source, thermocouple, and a pilot tube typically extend into the combustion chamber. When the temperature of the water in the tank falls below a set minimum, fuel is introduced into the combustion chamber through the fuel manifold tube and burner element. This fuel is ignited by the pilot flame or other ignition source, and the flame is maintained around the burner element. Air is drawn into the plenum, sometimes assisted by a blower, and the air mixes with the fuel to support combustion within the combustion chamber. The products of combustion typically flow through a flue or heat exchange tube in the water tank to heat the water by convection and conduction.
In some cases, a water heater may be positioned in an area that is also occupied by lawnmowers, chain saws, snow blowers, trimmers, paint, and/or other equipment and/or chemicals. In such cases, it is not uncommon for gasoline and/or other flammable substances (e.g., kerosene, diesel, turpentine, solvents, alcohol, propane, methane, butane, etc.) to be present in the same area. Such flammable substances can emit flammable vapors.
If the flammable substances are mishandled, the flammable vapors may encounter an ignition source, such as the pilot flame or burner flame of a fuel-fired water heater. As a result of the mishandling of flammable substances, the flammable vapors may ignite, and the flame may follow the flammable vapors to their source, causing an explosion and/or a fire. Consequently, various attempts have been made at producing water heaters and other fuel fired appliances that are less prone to igniting flammable vapors. A need remains, however, for appliances such as water heaters that are more immune to external flammable vapors. A need also remains for appliances such as water heaters that are more immune to igniting external flammable vapors while resisting unnecessary lockouts.